Soft tissues, such as ligaments, tendons and muscles, are attached to a large portion of the human skeleton. In particular, many ligaments and tendons are attached to the bones which form joints, such as shoulder and knee joints. A variety of injuries and conditions require attachment or reattachment of a soft tissue to bone. For example, when otherwise healthy tissue has been torn away from a bone, surgery is often required to reattach the tissue to the bone to allow healing and a natural reattachment to occur.
In the case of a partial detachment, the injury frequently heals itself if given sufficient time, and if care is taken not to expose the injury to undue stress during the healing process. If, however, the ligament or tendon is completely detached from its associated bone or bones, or if it is severed as the result of a traumatic injury, partial or permanent disability may result. Fortunately, a number of surgical procedures exist for reattaching such detached tissues and/or completely replacing severely damaged tissues. Typically, these procedures can involve the re-attachment of the detached tissue using attachment devices such as staples, sutures and/or cancellous bone screws. Such attachment devices have also been used to attach tendon or ligament grafts (often formed from autogeneic tissue harvested from elsewhere in the body) to the desired bone or bones.
A common injury where treatment requires the reattachment of soft tissue to bone is anterior cruciate ligament (ACL) damage in a human knee. Several methods for repairing an ACL injury are known in the art, and typically involve the replacement of the damaged or torn ligament with a tissue graft by first forming bone tunnels through the tibia and/or femur at the points of normal attachment of the anterior cruciate ligament. Next, a ligament graft is harvested and prepared for insertion into the bone tunnel. The graft can be folded over and secured at its folded end to a graft anchor device using suture thread. For instance, a graft attachment device can be used to anchor the folded end of the graft to the femur. In a typical graft attachment device, the folded end is held to the graft anchor device by a suture thread, while the graft attachment device is anchored to the femur outside the bone tunnel exit. Then, a screw or cross pin is inserted through the bone tunnel and graft so as to intersect through the bone tunnel and secure the graft in position within the tunnel by a tight interference fit. The pin compresses and suspends the graft at this graft-tunnel interface. Finally, the free end of the graft ligament is securely attached to the tibia.
An alternative method for securing a graft inside a bone tunnel of a femur involves inserting a folded graft, folded end first, into a bone tunnel, and then securing the folded end by placing a cross pin through the graft and between the folds. Often, the graft is also stitched together, folded over, and the ends whip stitched to form a graft bundle. Since the graft is essentially folded over the cross pin inside the bone tunnel, the graft acts as a “slingshot” and can therefore stretch and bend during flexion of the knee joint. An additional cross pin can optionally be inserted to additionally secure the graft to the femur.
In order to provide for proper cross-pinning of the graft in the bone tunnel, a drill guide is generally used. The drill guide serves to ensure that the pin transversely passes the bone so that it will intersect the appropriate tunnel section and the graft. Drill guides for use in effecting such transverse drilling, as well as methods for using such guides in an ACL repair surgery, are described, for example, in U.S. Pat. Nos. 6,540,783, 6,517,546, 6,379,384, 6,113,604, 6,066,173, and 5,849,013, all of which are hereby incorporated by reference.
A potential problem with the current techniques for femoral fixation of a soft tissue graft during ligament (e.g., ACL) reconstruction surgery is that the point of fixation, i.e., where the graft is secured, is relatively far from the joint line. That is, the graft is secured relatively near the bone tunnel exit. Because the graft is not-compressed and suspended near the bone tunnel entrance, the graft does not reside in a tight interference fit at this portion of the bone tunnel. During flexion and movement of the knee joint, this unsecured portion of the graft tends to sway back and, forth, causing a “windshield wiper” effect that can ultimately result in the erosion and weakening of the graft near the joint line. Often referred to as the “bungie cord” effect, this swaying motion can also lead to tunnel widening. Furthermore, if the graft does not form a tight fit with: the bone tunnel at the entrance, synovial fluid can enter, the tunnel and impregnate the graft and thus render the graft ineffective.